Plasma processing apparatus and a plasma processing method

ABSTRACT

In an oxide film etching process, a plasma having a suitable ratio of CF 3 , CF 2 , CF, and F is necessary, and there is a problem in that the etching characteristic fluctuates in accordance with a temperature fluctuation of the etching chamber. Using a UHF type ECR plasma etching apparatus having a low electron temperature, a suitable dissociation can be obtained, and by maintaining the temperature of a side wall of the etching chamber in a range from 10° C. and 120° C., a stable etching characteristic can be obtained. Since oxide film etching using a low electron temperature and a high density plasma can be obtained, an etching result having a superior characteristic can be obtained, and, also, since the side wall temperature adjustment range is low, a simplified apparatus structure and a heat resistant performance countermeasure can be obtained easily.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of application Ser. No.11/348,300, filed Feb. 7, 2006, which is a Continuation application ofapplication Ser. No. 09/414,520, filed Oct. 8, 1999, the contents ofwhich are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a plasma processing apparatus and aplasma processing method and in particularly to an apparatus for etchingan insulation film such as a silicon oxide film of a wafer using aplasma and relates to a plasma etching apparatus and a plasma etchingmethod having a plasma generation source which can be corresponded to aminute practicing of an etching pattern and further enable formaintaining a stable etching characteristic during a long period.

Among conventional plasma processing apparatuses, an oxide film plasmaetching apparatus is exemplified and techniques and problems of thisapparatus are shown. As the conventional plasma source of an oxide filmuse etching apparatus, a type which is used most widely is a narrowelectrode type high frequency plasma generation apparatus which iscomprised of a pair of opposing electrodes.

The systems of the narrow electrode type high frequency plasmageneration apparatus have known that 25 there is a system in which ahigh frequency having from 13.56 MHZ to a several 10 MHZ degree isapplied to one electrode and to another electrode by mounting a wafer ahigh frequency bias of about 1 MHZ is applied separately to theelectrode on which a wafer is mounted, and there is another system inwhich a high frequency is applied to the pair of electrodes.

In this narrow electrode type of plasma source etching apparatus, sincethe distance between the electrodes is narrow, for example, from 20 mmto 30 mm, it is known as a narrow electrode type plasma source and aparallel flat plate type plasma source. Further, in the narrow electrodetype plasma source, it is difficult to generate a plasma in a regionwhere the pressure is low, however, by the addition of a magnetic field,an apparatus is obtained in which a lowering of the discharge pressurecan be achieved.

In addition to the above-stated narrow electrode type of apparatus,other plasma etching apparatuses have been known. These apparatusesinclude a plasma etching apparatus having an induction type plasmasource in which an induction coil is used and another plasma etchingapparatus in which a plasma etching microwave is introduced. In theseapparatuses having an induction type etching source and a microwave typeplasma source, it is possible to generate and maintain the plasma undera low pressure; and, since the plasma density is high, such a plasmasource is known as a low pressure and a high density plasma source.

In silicon oxide film etching, as an etching gas, a mixture gas, inwhich argon (Ar), a gas including carbon (C) and fluorine (F), such asC₄F₈, and a gas including hydrogen (H), such as CHF₃, are mixed, isused; and, further, another mixture gas, in which oxygen (O₂) and carbonmonoxide (CO) and hydrogen (H₂) etc. are added to the above-statedmixture gas, is used. These gases are dissociated by the plasma and aredissolved to form CF₃, CF₂, CF, and F. The amount and the ratio of thisgas molecule species exerts a large influence on the etchingcharacteristic of the silicon oxide film (hereinafter, it will bereferred to merely as an “oxide film”).

In particular, in the case of a high density plasma source, since theelectron temperature in the plasma is high, plasma dissociationprogresses, and the plasma comes to have many fluorine gas molecules F.Further, as the ionization progresses, the ratio of neutral gas moleculespecies (radicals) becomes low. For these reasons, in oxide film etchingwith a high electron temperature and a high density plasma, since theamount of CFx (CF₃, CF₂, CF) which adheres to a silicon surface, whichis a foundation of the oxide film, is lowered, there are problems inthat the etching-speed of the silicon (Si) is large and the selectionratio is small.

As means for solving the above stated problems, a method for increasingthe CFx radical amount in the plasma has been known, in which thetemperature of the wall face of the etching chamber is raised to about200° C., in an effort to discharge the deposition film which has adheredto the wall face by reducing the adhesion of the deposition film to thewall face of the etching chamber. As a result, in an apparatus in whicha high density plasma is used, to obtain the desired selection ratio, ahigh temperature performance of the wall face of the etching chamberbecomes indispensable.

An oxide film etching apparatus described in Japanese application patentlaid-open publication No. Hei 7-183283 is an example of an apparatus inwhich a wall face of an etching chamber is formed to have a hightemperature performance.

As a countermeasure for obtaining the high selection ratio in additionto the above technique, there is a known method in which the electrontemperature in the plasma is lowered and plasma dissociation isrestrained. More specifically, in this method the plasma application iscarried out intermittently, and so this method is called a pulse plasmamethod.

As another one example of obtaining a high selection ratio, there is amethod in which materials for consuming fluorine (F) are installed in anetching 25, chamber in advance. In Japanese application patent laid-openpublication No. Hei 9-283494, such a method is described, in which aside wall of an etching chamber is constituted by silicon (Si), and aheating means for heating the side wall and a bias application means areprovided, so that the fluorine (F) in the plasma is consumed.

In oxide film etching in which narrow electrode type of plasmageneration is used, in correspondence with the fine patterning in whicha device pattern size is less than 0.25 μm, it is necessary to make thescattering of the ion incident angle at a portion to be subjected to theetching extremely small. Since the scattering of the ion incident anglecauses an abnormality of the etching shape and a decrease in the numberof ions reaching the bottom of a deep hole, problems are causedincluding a lowering of the etching speed and a premature stopping ofthe etching in the formation of holes. This scattering of the ionincident angle is caused by the incident angle distribution having aspread angle because the ions collide with radicals in the plasma.

To solve the above-stated problems, it is effective to decrease thenumber of collisions between ions and radicals; more particularly, it isnecessary to lower the pressure. As a result, in the narrow electrodetype of plasma generation apparatus, because it is difficult to carryout the plasma discharge under low pressure conditions, even under a lowpressure sufficient to generate a plasma, it is proposed that thefrequency of the plasma generation source be made high and that amagnetic field be applied.

Further, in the narrow electrode type of plasma source in which thedistance between the electrodes is narrow, in a case where a lowpressure is used, since the average free path distance of the gasmolecules becomes long, the collision frequency of the gas molecules isdecreased, and, in place of this, the collision between the gasmolecules and the electrode becomes dominant.

This is not a preferable condition, since, in the etching apparatus,according to the collision of the gas molecules in the plasma, it isnecessary to control the maintenance and the reaction of the plasma;and, as a result, in order to accommodate a low pressurization, it isnecessary to provide a large electrode interval.

When the electrode interval is wide, the surface area of the side wallin the etching chamber becomes large. Here, the surface of the etchingchamber is the surface which is subjected to the plasma, and the surfacedoes not include a surface of the top plate (ceiling), a surface of thefloor, and a surface of the electrode (the wafer).

Until now, in the narrow electrode type plasma source, from the aspectof the plasma and a wafer, since the side wall area is narrow, thedeposition and the gas discharge at the side wall have almost noinfluence on the etching characteristic; however, in the narrowelectrode type plasma apparatus in which a low pressurization is used,it is necessary to take a new countermeasure.

Further, to accommodate a large diameter wafer, it is necessary to makethe gas pressure distribution across the wafer face and the reactionproduct distribution uniform; and, for this purpose, it is necessary toprovide a wide electrode interval, and so the area ratio of the sidewall becomes more and more important.

The influence of the affects of the reaction products which adhere tothe side wall on the etching characteristic is discussed above, however,when the etching is continued over a long period of time, a change ofthe influence becomes a problem. For example, by repeatedly carrying outetching operation, the temperature of the side wall will rise gradually.When the temperature of the side wall has risen sufficiently, thecharacteristic of the adhesion and adsorption of the reaction productson the side wall is changed, and, as a result, the etchingcharacteristic fluctuates.

Further, in a case where the amount of the deposition film on the sidewall accompanying the etching is increased gradually, in accordance withthe dependence on the amount of the deposition film, it is possible tochange the desorption and adsorption characteristic of the reactionproducts at the side wall surface.

A phenomenon in which the etching characteristic is influenced by thetime lapse change stated above is known particularly in the case ofoxide film etching. As a result, the temperature change of the side wallin the oxide film etching apparatus represents an important problem.

In particular, in a high electron temperature and high density plasmasource, it is necessary to establish a high side wall temperature. Inthe case of a high side. wall temperature, even the side walltemperature fluctuates a little, and so the adsorption and desorptioncharacteristic of the deposition film is changed largely. For thesereasons, it is necessary to restrain the side wall temperaturefluctuation to a small range, and a high accuracy temperatureadjustment, such as 200° C.±2° C. needs to be carried out.

As stated above, in any of the plasma sources, to satisfy therequirement for oxide film etching, namely. for obtaining a high etchingspeed, while attaining a high selection ratio, low micro loading, andthe passing-through of a deep hole, there still remain problems to besolved.

The important problem in an oxide film etching apparatus involves thedissociation of the gas molecules as the plasma is being formed underthe most suitable conditions for the etching of the oxide film. Toaddress this problem, a new plasma generation source producing a highdensity plasma under a low electron temperature has been proposed. Forexample, Japanese application patent laid-open publication No. Hei8-300039, discloses a UHF type ECR apparatus having a plasma excitationfrequency in the UHF band from 300 MHZ to 1 GHz. The electrontemperature of the plasma which is excited in the frequency band in theabove stated range is low, for example, from 0.25 eV to 1 eV, and theplasma dissociation of C₄F₈ is at a level suitable to oxide filmetching. Further, since it is an ECR.(Electron Cyclotron Resonance)system, even under a low pressure, it is possible to generate a highdensity plasma.

As stated above, for achieving fine patterning on a wafer of largediameter, it is necessary to make the electron temperature low and toprevent an excessive dissociation of the etching gas, and further tomake the plasma density high. Further, it is necessary to make theplasma density, the gas pressure and the reaction product distributionon the wafer uniform; and, as a result, it is necessary to provide anapparatus in which the oxide film etching characteristic is not changedover a long period of operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a plasma processingapparatus and a plasma processing method, wherein, using a UHF type ECRplasma etching apparatus to generate a high density plasma under a lowelectron temperature necessary for oxide film etching etc., a prematurestopping of the etching does not occur, and in which a stable operationor a stable processing can be carried out.

The characteristic feature according to the present invention resides ina plasma processing apparatus and in a plasma processing method using avacuum processing chamber, a sample table for mounting a sample which isprocessed in said vacuum processing chamber, and a plasma generationmeans, wherein, when plasma processing is carried out by generating aplasma by introduction of a gas which contains at least carbon andfluorine into the processing chamber, and by which a gas species isgenerated which contains carbon and fluorine according to a plasmadissociation, said plasma generation means being a plasma generationmeans in which the degree of plasma dissociation is in a middle rangeand said gas species containing carbon and fluorine is generated fullyin the plasma, and wherein the temperature of a region which forms aside wall of said vacuum processing chamber is controlled to have arange of 10° C. to 120° C.

In a UHF type ECR plasma etching apparatus having a UHF band microwaveradiation antenna disposed at a position opposite to the wafer, anetching gas is supplied from a gas supply portion provided on an antennaportion. The UHF band microwave is radiated directly to the plasma fromthe antenna and is radiated in the plasma through a dielectric bodywhich is provided at a periphery of the antenna.

In an electrode for mounting the wafer (a wafer mount electrode or alower electrode), an etching position and a wafer delivery position arelocated at separate locations, and an electrode raising and loweringfunction is provided. A distance (called an “electrode interval”)between the wafer mount electrode and the antenna or the gas supplyplate is established as 50 mm to 100 mm taking into considerationre-association of the reaction products.

According to the plasma processing apparatus, a side wall temperature ata periphery of the electrode is temperature adjusted within a range of10° C. to 120° C., preferably a range of 30° C. to 50° C. As the sidewall temperature fluctuates, a gas species is discharged from adeposition film on the side wall, and this has an influence on theetching characteristic.

In accordance with the present invention, to restrain the above-statedinfluence, the temperature control accuracy of the side wall iscontrolled to ±5° C. Since the side wall temperature is low, even whenthe temperature of the side wall fluctuates by 5° C. degree, thefluctuation of a discharge gas amount which is discharged from the sidewall will be small, so that the influence on the etching characteristiccan be neglected.

Further, since the plasma source is a UHF type ECR system, the plasmadissociation is in a middle range and a CFx species exists fully to alevel necessary for the oxide film etching. Since the problem of ashortage of CFx species and an excess F, which is inherent in a highdensity plasma source, can be solved, to increase the selection ratio,it is unnecessary to increase the side wall temperature.

Herein, when the dissociation is excessive, F or C becomes rich, andwhen the dissociation is insufficient, there is a shortage of F, CF₂,CF₃, etc; accordingly, it is desirable to have a plasma dissociationfall in middle range. Further, since the side wall temperature iscontrolled to a low temperature, with a side wall temperature controlaccuracy of ±5° C., the fluctuation of the etching characteristic can berestrained for a long period of operation.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional diagram showing an etching apparatus ofa plasma processing system representing one embodiment according to thepresent invention;

FIG. 2 is a graph showing a size relationship of various kinds of plasmasources of a plasma processing apparatus and a plasma processing methodaccording to the present invention;

FIG. 3 is a graph showing a characteristic of a gas discharge from adeposition film of a plasma source of a plasma processing apparatus anda plasma processing method according to the present invention;

FIG. 4 is a graph showing the influence of a side wall temperature on atime lapse change of a plasma source of a plasma processing apparatusand a plasma processing method according to the present invention;

FIG. 5 is a graph showing an etching speed change in a case where atemperature adjustment of a side wall is not performed; and

FIG. 6 is a graph showing an etching speed change in a case where atemperature adjustment of a side wall is performed according to thepresent invention.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

Hereinafter, a plasma processing apparatus and a plasma processingmethod representing one embodiment according to the present inventionwill be explained.

FIG. 1 is an example of a UHF type ECR plasma etching apparatus. At aperipheral portion of an etching chamber 1 (a vacuum processingchamber), which is operated as a vacuum vessel, a coil 2 is installed,and this coil 2 generates an electron cyclotron resonance (ECR) field.An etching gas is supplied from a gas supply pipe 3 and is introducedvia a gas supply plate 4 to the etching chamber 1. The gas supply plate4 is comprised of a plate made of silicon or a glass form carbon inwhich about 100 fine holes having a diameter of from 0.4 mm to 0.5 mmdegree are provided.

At an upper portion of the gas supply plate 4, a disc-shaped antenna 5is provided, and this antenna 5 radiates microwave energy in the UHFband. The microwave energy is supplied to the antenna 5 from a powersupply 6 through an induction shaft 7. When the microwave energy isradiated from a periphery of the antenna 5, an oscillating electricfield in a space above the antenna 5 is introduced into the etchingchamber 1 through a dielectric body 8. Further, between the antenna 5and an electrode 9, a volume combination electric field is generated,and this electric field becomes an effective plasma generation source.The frequency of the microwave energy is set to a range of from 300 MHZto 1 GHz and has a band area in which the electron temperature of theplasma is a low temperature of from 0.25 eV to 1 eV.

In this embodiment according to the present invention, a frequency bandin the vicinity of 450 MHZ can be employed. Further, as the dielectricbody 8, a quartz or an alumina material can be employed. Further, a heatresistant polymer having a small dielectric loss, such as a polyimideetc., can be employed as well.

The electrode for mounting a wafer (the wafer mount electrode or sampletable) 9 is provided below the gas supply plate 4, and a wafer 10representing a sample is supported on the sample table through aelectrostatic adsorption. To draw the ions in the plasma to the wafer10, a high frequency bias is applied to the wafer mount electrode 9 froma high frequency power supply 11.

Further, the temperature control of an inner wall of the etching chamber1, representing the vacuum processing chamber, which is an essentialfeature according to the present invention, is carried out at atemperature adjustment side wall 12 of the etching chamber 1. To thetemperature adjustment side wall 12, although not shown in the figure, acoolant medium which is temperature controlled is introduced, so thatthe temperature adjustment side wall 12 is maintained at a constanttemperature. In this embodiment according to the present invention, theconstant temperature in the temperature adjustment side wall 12 is setto 30° C.

The etching gas and reaction products are deposited on the inner wall ofthe etching chamber 1 and they are also deposited at the periphery andin a downstream area of the wafer mount electrode 9, so that adeposition film is generated which is the origin of the foreign matterin the etching chamber 1. Accordingly, it is necessary to periodicallyremove the deposition film, however, it is not always easy to remove astrongly adhered deposition film. Herein, in this embodiment accordingto the present invention, the cleaning of the deposition film is carriedout using an exclusive cleaning apparatus.

The time used for establishing a vacuum state by evacuation of theetching chamber 1, which has been opened to the air for cleaning, isimportant from an aspect of the non-operation time of the apparatus andfurther from an aspect of an improvement of the productivity of theapparatus. Accordingly, it is desirable to prevent the deposition filmfrom adhering on a portion where a component exchange-over is notcarried out easily, and to try to provide the component to which thedeposition film has adhered as a component which can be easily replacedby another clean component. In this way, the opening time for cleaningin the etching chamber 1 can be shortened, and a reduction of thecleaning and evacuation time can be achieved.

In this embodiment according to the present invention, to prevent thedeposition film from-adhering to the downstream region of the etchingchamber 1, a deposition film cover 13 is provided in the downstreamregion of the temperature adjustment side wall 12 of the etching chamber1. To the cover 13, a vacuum evacuation and wafer delivery openingportion is provided. Since the deposition film can be removed with thiscover 13, the adhesion of the deposition film in the downstream regionof the temperature adjustment side wall 12 can be reduced.

A vacuum chamber 15 is connected directly to the etching chamber 1, anda turbo molecular pump 14 having an evacuation speed of from 2000 L/s to3000 L/s is installed in the vacuum chamber 15. Further, although notshown in the figure, to an opening portion of the turbo molecular pump14, a vacuum evacuation speed adjustment conductance valve 16 isinstalled, and this evacuation speed adjustment conductance valve 16 isused for separating the turbo molecular pump 14 during the chamber opentime, or the evacuation speed adjustment conductance valve 16 is usedfor not opening the chamber to the air.

Next, an example of oxide film etching using the plasma processingapparatus of this embodiment according to the present invention will beexplained.

To the etching chamber 1 which is evacuated to a high vacuum condition,although not shown in the figure, the wafer 10 is carried in from atransfer chamber by a transfer arm, and the wafer 10 is delivered ontothe wafer mount electrode 9. The transfer arm is then retracted, and,after a valve arranged between the etching chamber 1 and a transferchamber has been closed, the wafer mount electrode 9 is raised to aposition where the etching is to be carried out. In the case of thisembodiment according to the present invention, the distance between thewafer 10 and the gas introduction plate 4 (an electrode interval) is setto from 50 mm to 100 mm.

As the etching gas, a mixture gas comprised of Ar, and C₄F₈, and O₂ isused, and the respective flow amounts are 500 sccm, 10 sccm and 5 sccm.The pressure of the etching gas is 2 Pa. The output of the UHF microwavepower supply 6 is 1 kW, and the output of a bias power supply 11 to thewafer 10 is 600 W.

A current is applied to the coil 2 and a resonance magnetic field having0.016 T of UHF energy at 450 MHZ is generated between the gas supplyplate 4 and the wafer mount electrode 9 (namely the wafer 10). Next, themicrowave power supply 6 is operated. Due to the electron cyclotronresonance phenomenon, a strong plasma is generated in the ECR areahaving a resonance magnetic field strength of 0.016 T.

To improve the uniformity of the etching characteristic, it is necessaryto ensure that the incident ion density on the surface of the wafer 10is uniform, and, when the ECR is positioned as stated above and theshape of the ECR area is formed with a raised portion extending towardthe wafer 10, the required uniformity of the ion current density can beattained.

After a spark of the plasma, not shown in-the figure, from a directcurrent power supply which is connected directly in parallel with thehigh frequency power supply 11, a high voltage is applied to the wafermount electrode 9, and then the wafer 10 is electrostatically attractedto and held on the wafer mount electrode 9.

At a rear face of the wafer 10, helium (He) gas is introduced, and thetemperature adjustment of the wafer 10 is carried out between the wafermounting face of the wafer mount electrode 9, which is temperaturecontrolled by a coolant medium, and the wafer 10, through the helium(He) gas.

Next, the high frequency power supply 11 is operated, and a highfrequency bias is applied to the wafer mount electrode 9. Accordingly,ions are incident vertically from the plasma onto the wafer 10. In oxidefilm etching, it is necessary to carry out a processing with high energyions.

In this embodiment, according to the present invention, a high frequencybias voltage Vpp (the voltage between the maximum peak and the minimumpeak) has a value of from 1000 V to 2000 V. In response to the impact ofhigh energy ions with the wafer surface, the temperature of the wafer 10rises. In oxide film etching, since the selection ratio is high athigher temperature values, the etching characteristic has a superiorcharacteristic, and so the wafer temperature is adjusted to a value ofseveral 10° C. However, since it is necessary to carry out theprocessing with high energy ions, the heat input amount to the wafer 10is large, and so the coolant medium temperature of the wafer mountelectrode 9 is set in the vicinity of −20° C.

At this time, when the bias voltage is applied to the wafer 10, theetching is started, and the etching is finished within a predeterminedetching time. Or, though not shown in the figure, by monitoring theplasma luminescence strength change of the reaction products and furtherjudging the finish point of the etching, an etching finish time can bedetermined, and, after a suitable over etching has been performed, thenthe etching is finished. The etching is completed at a time when theapplication of the high frequency bias voltage is stopped.Simultaneously with this, the supply of the etching gas is stopped.

However, it is necessary to provide a process in which theelectrostatically held wafer 10 is released from the wafer mountelectrode 9, and, for this purpose, an electric adsorption gas, such asAr etc., is supplied. By stopping the supply of the electrostaticadsorption voltage, and then connecting the electric supply line to anearth ground, while maintaining the discharge of the microwave energy,an electric adsorption time of 10 seconds is allocated. Accordingly, theelectric charges on the wafer 10 are adsorbed by the earth groundthrough the plasma, and, as a result, the wafer 10 can be removedeasily.

When the electric adsorption process is ended, the supply of theelectric adsorption gas is stopped, and also the supply of the microwaveenergy is stopped. Further, the current supply to the coil 2 is stopped.Further, the wafer mount electrode 9 is lowered until the surfacethereof reaches the wafer delivery position.

After that, for some time, the etching chamber 1 is evacuated until highvacuum is achieved. At a time point when the high vacuum state has beenreached, the valve between the etching chamber 1 and the transferchamber is opened, the transfer arm is inserted therein and then thewaver 10 is carried out. In case there is to be a next etching process,a new wafer is carried in and the etching is performed again accordingto the above-stated procedures.

In the above description, the representative flow of the etching processwas explained.

The electron temperature of the UHF band microwave ECR plasma is in arange of from 0.25 eV to 1 eV and the dissociation of C₄F₈, which is theetching gas, does not progress much. The dissociation of C₄F₈ is acomplicated process, in which the gas species which contributes to theetching is first dissociated from CF₃ to CF₂, then CF is generated, andfinally F is generated. As a result, the higher the electrontemperature, the more the plasma becomes rich in F.

As stated in the Background of the Invention, to ensure the properselection ratio in the oxide film etching, in the deposition of a filmon the foundation silicon, it is necessary to restrain the etchingaccording to the high incident ion energy. Namely, since high energyions are incident on the wafer, when there is no deposition film, thereis a possibility that the etching will progress according to a physicalsputter.

As a result, for the etching to progress, it is necessary to supply highenergy ions to the bottom of a hole, however to ensure the requiredselection ratio, it is necessary to supply radicals which form adeposition film. It is said that the radicals for forming the depositionfilm are CF₃ and CF₂.

On the other hand, F radicals form SiF₄ etc. and the foundation siliconis caused to be etched. As a result, to perform high selection ratioetching, it is necessary to make CF₂/F (CF₂-F ratio) large. In the caseof UHF band microwave ECR plasma, since the electron temperature is low,the generation amount of F is small, and a plasma having a plentifulamount of CF₃, CF₂ and CF is formed.

Accordingly, as shown in the case of a high electron temperature and ahigh density plasma, to supply CF₂ and CF₃, which become insufficientdue to the excessive progress of the dissociation of the plasma, it isunnecessary to heat the inner wall of the etching chamber 1 to more than200° C.

As the necessary points for achieving a fine processing correspondenceetching, the following points are stated, namely (1) under a lowelectron temperature, the plasma dissociation is restrained suitably anda plasma having a large CF₂/CF (CF₂-CF ratio) is generated; (2) thediscrepancy between a 90° angle and the ion incident angle is restrainedto a small value and a tapering formation of the etching shape; and (3)even when the etching is repeated many times, the fluctuation of theetching characteristic is small.

In addition to the above, an item relating to the etchingcharacteristics is an important development problem, however, in thepresent specification, such an item is not mentioned.

The above-stated item (1) for the necessary points for the fineprocessing correspondence etching is solved by the use of the UHF bandmicrowave plasma etching apparatus according to the present invention.

As to the above-stated item (2) for the necessary points for the finepracticing correspondence etching, a main cause is that the orbit of theions is displaced with the collision of the ions and a gas molecule inthe vapor phase, and so it is effective to lower the pressure to lessenthe occurrence of such collisions. Since the UHF band microwave plasmaetching apparatus according to the present invention cases electroncyclotron resonance, it is possible to generate the plasma under a lowpressure.

As to the above-stated item (3) for the necessary points for the fineprocessing correspondence etching, it is necessary to preventfluctuation of the etching characteristic even when the number ofetching operations which are repeated is in the order of severalhundred; namely, it is necessary to restrain the time lapse change. Amain cause of the time lapse change is the time fluctuation of the kindsof gas which are discharged from the deposition film which adheres tothe inner wall (the side wall, the ceiling, etc) and the othercomponents of the etching chamber 1. More specifically, the temperaturefluctuation of the members to be subjected to the processing, such asthe side wall, represents a large cause of the problem.

As a countermeasure against the restraint of the time lapse change,basically the apparatus is formed so as to prevent fluctuation of thedesorption and adsorption phenomenon of the deposition film on the wallface using temperature control; however, in various plasma generationsystems, the wall face area used to form the apparatus differs.

The relationship between the etching chamber height and the side facearea is shown in FIG. 2. In the narrow electrode plasma type apparatus,the height of the etching chamber is low, and also the area of the sidewall face is narrow. On the other hand, in the high density plasmaapparatus, the height of the etching chamber is-high, and also the areaof the side wall face is wide.

In the UHF type ECR apparatus according to the present invention, theheight of the etching chamber (the electrode interval) and the area ofthe side wall are positioned intermediately relative to the other typesof apparatus, and the apparatus occupies a region which is suitable foroxide film etching. Namely, according to the present invention, theheight of the etching chamber (the electrode interval) and the area ofthe side wall has a middle value in the 30 mm −100 mm range of thenarrow electrode (about 30 mm) and the microwave ECR induction type(more than 100 mm). The height of the etching chamber, namely theelectrode interval, is a distance of from 50 mm to 100 mm, and thereaction products generated by the etching are re-dissociated andre-incident on the wafer 10.

For the above stated reasons, the etching characteristic of the oxidefilm is influenced, however, this is caused by making the most suitableperformance to the influence degree, such as the re-dissociation and theincidence of the reaction products etc. with the etching characteristicof the oxide film. Namely, in this embodiment according to the presentinvention, the electrode interval is set to a predetermined distancewhich is determined by a relative relationship of the mean free ion pathin the vicinity at a pressure of 2 Pa.

Since the electrode interval is set to the above stated distance, thepressure distribution on the face of the wafer 10 can be made uniform.In a case where the wafer diameter is large, such-as from 200 mm to 300mm, the difference in pressure between the center and the periphery ofthe wafer 10 can be small. Further, since the conductance, which dependson the electrode interval, is large, a high speed of evacuation of thechamber 1 to a high vacuum can be attained, and, as a result, the timeduring which the etching gas and the reaction products remain in thechamber.

In a case where the area of the side wall is further widened, there is apossibility that the adhesion amount of the deposition film becomeslarge, with the result that the degree of influence on the etchingcharacteristic becomes large. In an apparatus for maintaining a highdensity plasma, according to the requirements of the plasma generationmethod, it is necessary to form the height of the etching chamber tofall in a range from 100 mm to 200 mm. Accordingly, the ratio of thearea of the side wall to the whole area of the etching chamber is high,and so the influence on the fluctuation of the etching characteristic bythe etching gas and the deposition of the reaction products on the sidewall will be large.

As methods for restraining this influence, there are methods in whichthe temperature fluctuation of the side wall is reduced or the side wallis heated to a high temperature to prevent a deposition film fromadhering thereto.

Further, as stated above, in an apparatus using a high density plasmasource, since the electron temperature is high, an F-rich plasma isgenerated. Therefore, to ensure a proper selection ratio, it isnecessary to reduce the gas species which adheres to the side wall, orit is necessary to promote a gas discharge from the deposition film. Asa result, it is necessary to raise the side wall to a high temperature.

For the above stated reasons, in a high electron temperature and highdensity plasma etching apparatus, the side wall is heated to 200° C.degree and the temperature fluctuation is maintained within a range of±2° C. However, it is difficult technically to heat the side wall to ahigh temperature of more than 200° C., and it is also difficulttechnically to restrain, with high accuracy, the temperature fluctuationto as little as ±2° C. Further, such a technique invites a complicatedstructure for the apparatus and a problem in reliability, as well as anincrease in cost. Further, the side wall comprises the entire inner wallof the etching chamber, and includes the top plate and other portionswhich contact the plasma.

In a portion where the deposition film adheres, but which is notcontacted directly by the plasma, since this portion has a possibilityfor affecting the etching characteristic, it is necessary to take suchportion fully into consideration. Further, in the apparatus according tothe present invention, since the side wall is from 5.0 mm to 100 mm, thedownstream region therefore can hardly comprise a region where thedeposition film is adhered. As a result, for oxide film plasma etching,it is desirable to provide an apparatus in which fluctuation of theetching characteristic is not generated, even when the temperatureadjustment accuracy in the control of the side wall temperature ismitigated.

In the UHF type ECR plasma apparatus according to the present invention,it is unnecessary to increase the side wall temperature to improve theselection ratio. There is the advantage that the side wall temperaturecan be established from the view point of the restraint of the timelapse change.

FIG. 3 shows the results in a case in which the temperature of thedeposition film was changed 1° C., and the gas discharge amounts fromthe deposition film were measured. It is seen from these results thatwhen the temperature of the deposition film is high, a large amount ofgas is discharged with a temperature fluctuation of 1° C. It is supposedthat when the gas which corresponds to the flow amount of 0.01 sccm bythe conversion calculation of the flow amount of the etching gas, thereis a possibility that the etching characteristic is influenced, and thetemperature adjustment range of the side wall temperature at this timeis shown on the right side in FIG. 3.

In the case of a wall temperature of 200° C., when the side wall is notcontrolled to ±2° C., the fluctuation of the gas discharge amountbecomes less than 0.01 sccm. On the other hand, when the side walltemperature is controlled to less than 120° C., even the side walltemperature changes cause a small change in the gas discharge amount.Namely, it is understood that even when the control accuracy of the sidewall temperature ±5° C. and ±10° C., the gas discharge for giving aninfluence to the etching characteristic does not occur.

In the etching apparatus according to the present invention, the sidewall temperature is established within a range of from 10° C. to 120° C.Preferably, it is controlled from the room temperature 20° C. to 50° C.With this temperature range, since the etching chamber is not heated toa high temperature, there is the advantage that the size of theapparatus is small, and the materials used for the vacuum sealing andmaterials having a different thermal expansion coefficient can be usedfreely, and the temperature control can be performed easily.

According to the present invention, system is provided in which acoolant medium which is connected to the temperature adjustment means isintroduced to the side wall. By the employment of such a system, thetemperature control can be carried out to less than ±10° C.

Further, FIG. 3 shows the results in which the discharge amounts fromthe deposition film were measured. When the side wall temperaturereaches a high temperature of more than 200° C., since the adhesionamounts of the deposition film themselves become small, in an apparatushaving a high temperature control in which a deposition film does notadhere, as shown in the example of FIG. 3, substantial gas dischargeamounts become small.

The stability of the gas discharge amounts and the magnitude of thefluctuation amounts into which the consideration of the adhesion amountsis taken are shown in FIG. 4. In FIG. 4, the horizontal axis indicatesthe side wall temperature of the etching chamber, and the vertical axisindicates the relative magnitude of the deposition film amount, thedegree of influence on the time lapse change and the gas dischargeamount.

The gas discharge amount from the deposition film increases abruptly forside wall temperatures which exceed 200° C. On the other hand, theamount of the deposition film which adheres to the side wall (thedeposition speed) reduces gradually in proportion to an increase in thetemperature and decreases abruptly for temperatures in excess of 200° C.The reason for this is that when the temperature exceeds 200° C., andfurther when the temperature exceeds 300° C., the deposition film doesnot adhere to the side wall.

Accordingly, in the temperature range of the AREA 1 in FIG. 4, since theside wall temperature is low, the influence for referring to the etchingcharacteristic to the deposition film of the side wall is small.Further, in the AREA 3 in FIG. 4, since the temperature is high, the gasdischarge amount from the unit deposition film is large, however adeposition film will hardly adhere, and, as a result, the gas dischargeamount is small and the influence on the etching characteristic issmall.

However, in the AREA 2 in FIG. 4, which represents an intermediatetemperature range between AREA 1 and AREA 3, the deposition film iscomparatively large and the gas discharge amount is large, and, as aresult, the temperature fluctuation of the side wall has a largeinfluence on the etching characteristic.

Taking into consideration the above-stated points, to restrain the timelapse change, the side wall temperature is set to the AREA 1 or the AREA3. The temperature range of the AREA 1 is less than 120° C., and in theAREA 3, the temperature range is more than 200° C., while in the AREA 2the temperature range is from 120° C. to 200° C.

According to this embodiment of the present invention, the temperatureof the side wall is established in the temperature range of the AREA 1in FIG. 4. Further, from the above-described principle, the side walltemperature may be established in the low temperature range, however,taking into consideration the ease in establishing the temperature andproviding a coolant medium without creating condensation, the lowerlimitation temperature is set to 10° C.

FIG. 5 shows the etching speed fluctuation in a UHF type ECR plasmaetching apparatus in a case of using a mixture gas containing Ar andC₄F₈, and in which continuous etching is carried out. In this case, thetemperature adjustment of the side wall is not carried out, and so thetemperature fluctuation rises with the discharge time of the plasma to60° C. degree from room temperature. The temperature fluctuation is ±20°C. The etching speed of the silicon nitride at the etching starting timeis high, as a result of the fluctuation of the etching characteristic.

On the other hand, FIG. 6 shows the etching characteristic in a casewhere the temperature adjustment of the side wall is carried out. Afterthe etching chamber is opened to the air and evacuation of the chamberis carried out, but without covering the inner portion of the etchingchamber by the deposition film and also the process for presenting theregular state, immediately after the etching is started, the etchingcharacteristic is stable from the starting time of the etching, and thefluctuation after that is not hardly in evidence. Further, the side walltemperature fluctuation at this time is within ±5° C.

As understood from the above-stated results, in a UHF type ECR plasmaetching apparatus, by performing a temperature adjustment of the sidewall, an extremely stable etching characteristic can be obtained.Further, in this embodiment according to the present invention, it isassumed that a UHF type ECR plasma etching apparatus is used, however,when the plasma source is-suited for the etching of an oxide film, it isnot limited to a UHF type ECR plasma etching apparatus. Namely, when theelectron temperature in the plasma is the low, for example, an electrontemperature of less than 1 eV, and when a high density plasma is used,for example, it is possible to employ an apparatus using a pulse plasmasource in which the application of the microwave is carried outintermittedly.

Further, it is possible to employ an apparatus using a plasma source inwhich an induction type plasma, except for the fact that the microwaveis pulse driven. When the side wall of the etching chamber of theseplasma sources is established at a range of 10° C. to 120° C., it ispossible to obtain a superior oxide film etching characteristic, and,further, it is possible to exhibit a stable characteristic during a longperiod of operation.

Further, the temperature adjustment of the side wall is exemplified byusing a coolant medium, however the invention is not limited to the useof a coolant medium, since it can employ any one of the various types ofcompulsory cooling using water cooling and vapor cooling, a heater, orlamp heating using infrared rays.

To summarize, the temperature must be formed within the range of 10° C.to 120° C. With the above stated temperature range, even when thetemperature adjustment range of the side wall is ±5° C. degree, a fullystable etching characteristic can be obtained.

According to the etching characteristic, even when the temperatureadjustment range of the side wall is ±10° C., a stable etchingcharacteristic can be obtained, and the temperature adjustment can becarried out extremely easily.

According to the present invention, since a superior oxide film etchingcharacteristic can be obtained and a stable characteristic can beobtained during a long period of operation, the following advantages canbe expected.

Namely, the yield can be improved and the throughput can be improved.Further, since the temperature adjustment is established in a lowtemperature range of from 10° C. to 120° C., the inconvenience in whichthe size of the etching chamber is made large due to thermal expansioncan be avoided. For example, the line expansion coefficient of thealuminum alloy which is largely used in the etching chamber is24×10⁻⁶K⁻¹; on the other hand, for alumina and quartz, the respectiveline expansion coefficients are 6×10⁻⁶K⁻¹ and 0.41×10⁻⁶K⁻¹. Since theline expansion coefficients differ so much, when the etching chamber isheated to produce the plasma discharge or the etching chamber istemperature controlled compulsively at a high temperature, thedifferences in the sizes between the materials become large, making itnecessary to structurally design the chamber to avoid thermal expansion.

Further, the change in size of the vacuum sealing portion exerts aninfluence on the sealing characteristic, and the heat resistantperformance of the elastomer which forms the seal material also becomesa problem. When the temperature reduces a level of more than 150° C.,the possibility that the life of the seal material will be short becomeshigh.

As stated above, various problems are caused due to high temperature,and the addition of heat resistant performance structurally causes thecost of the apparatus to increase.

1. A plasma processing method of using a plasma processing apparatuscomprising a vacuum processing chamber, a sample table for mounting asample which is processed in said vacuum processing chamber, atemperature adjustment side wall of said vacuum processing chamber and aplasma generation means for generating a plasma according tointroduction of a gas which contains at least carbon and fluorine,thereby forming a gas species which contains carbon and fluorine byplasma dissociation and a plasma processing is carried out using saidplasma, the plasma processing method comprising the steps of: generatinga plasma which contains the formed gas species, of a reduced amount of Fand a greater amount of CF₃, CF₂ or CF as a ratio of the gas species, bycontrolling the electron temperature of said plasma generated to a rangeof from 0.25 eV to 1 eV, so as to perform an etching with an etchingcharacteristic of a predetermined selection ratio and a predeterminedetching speed, etching said sample having an insulating film as a filmto be processed, using said plasma, and controlling a temperature ofsaid temperature adjustment side wall to a range of 10° C. to 120° C.,thereby adhering deposits to the temperature adjustment side wall andcontrolling the amount of the gas released from the deposits so as torestrain a time lapse change of the etching characteristic.
 2. A plasmaprocessing method according to claim 1, wherein said plasma generationmeans is an electron cyclotron resonance system using a microwave at afrequency of from 300 MHz to 1 GHz.
 3. A plasma processing methodaccording to claim 2, wherein a temperature-adjusted coolant medium isused as a means for controlling the temperature of said temperature ofsaid temperature adjustment side wall so as to establish restraint ofthe time lapse change.
 4. A plasma processing method according to claim3, wherein the temperature of said temperature adjustment side wall iscontrolled to a range of 30° C. to 50° C.
 5. A plasma processing methodaccording to claim 1, wherein a temperature-adjusted coolant medium isused as a means for controlling the temperature of said temperatureadjustment side wall so as to establish restraint of the time lapsechange.
 6. A plasma processing method according to claim 1, wherein thetemperature of said temperature adjustment side wall is controlled to arange of 30° C. to 50° C. so as to establish restraint of the time lapsechange.
 7. A plasma processing method according to claim 1, wherein saidtemperature of said temperature adjustment side wall is controlled so asto restrain a time lapse change of the amount of the gas released fromthe deposits.